There exits a known hybrid drive device having an engine, a fluid clutch, a motor generator and a transmission apparatus. Furthermore, the hybrid drive device includes an oil pump for the transmission apparatus on a power transmission path between the engine and the transmission. For example, disclosed in JP2008-24298A is a hybrid drive device having a power train that includes an electric machine and a hydraulic pressure pump for the transmission apparatus (which will be hereinafter referred to as a transmission hydraulic pressure pump) between an engine and a transmission apparatus, which establishes variable gear ratio. The electric machine, which serves as a motor and a generator, is normally connected to a driving shaft of the transmission apparatus. Furthermore, the hybrid drive device disclosed in JP2008-24298A includes a torque converter and at least one switchable first clutch device, which are disposed between the engine and the transmission apparatus. The hydraulic pressure pump is connected to the torque converter.
According to the hybrid drive device disclosed in JP2008-24298A, in a case where a general torque converter having a lock-up mechanism (i.e. a lock-up torque converter) is adapted as the torque converter, an engine torque vibration inputted into the first clutch device and a torque resonance, which is generated in response to the engine torque vibration, are hard to be restricted. In order to restrict the occurrence of the vibration and the resonance, an additional damper may need to be provided between the engine and the first clutch device, in addition to a lock-up damper. In this case, a relatively large space for providing the additional damper needs to be ensured, which may further result in increasing manufacturing costs.
In a case where a normally open-type clutch (i.e. a clutch which turns to be in an engaged state when an electrification to the clutch is turned off) is adapted as the first clutch device, even if the engine is started by some other method while the electric machine (a motor generator) is not allowed to be driven, the transmission hydraulic pressure pump is not likely to be driven because the first clutch device is in an open state (i.e. a disengaged state). Accordingly, the vehicle may not start moving.
On the other hand, in a case where a normally closed-type clutch (i.e. a clutch which turns to be in a disengaged state when the electrification to the clutch is turned off) is adapted as the first clutch device, in a process of staring and moving the vehicle, it may be conceivable to start the vehicle in the manner where: firstly, the transmission hydraulic pressure pump is driven in response to a rotation of the electric machine (the motor generator); secondly, a gear ratio is established at the transmission apparatus in response to a generated hydraulic pressure; and then starts the vehicle by means of the torque converter. However, in this case, because the electric machine (the motor generator) is rotated while the first clutch device is in the engaged state, the engine is also rotated, which may result in generating a large pumping loss. Furthermore, even if the first clutch device is turned to be in the disengaged state after a sufficient hydraulic pressure is ensured and the vehicle starts moving, it may take a relatively long time in the process of staring and moving the vehicle, in other words, a responsiveness of the hybrid drive device may be deteriorated.
Furthermore, according to the hybrid drive device, which is disclosed in JP2008-24298A and which includes the torque converter, the electric machine (the motor generator) is arranged on the power train between the first clutch device and the torque converter. Therefore, in a case where regeneration is executed by the electric machine (the motor generator), a power transmitted from the transmission apparatus is reduced by the torque converter, so that the reduced power is transmitted to the electric machine (the motor generator). As a result, regeneration efficiency at the electric machine (the motor generator) is deteriorated.
A need thus exists to provide a hybrid drive device which is not susceptible to the drawback mentioned above.